1. Field of the Invention
The present invention relates to an exposure apparatus used for manufacturing a microdevice such as a semiconductor device or liquid crystal display device, a method of manufacturing a microdevice by using the exposure apparatus, and a method of manufacturing the exposure apparatus.
2. Related Background Art
One of microdevice manufacturing steps is an exposure step. Microdevices include those having a larger size such as liquid crystal display devices, for example. For exposure of such a microdevice, a screen synthesizing technique is used. In the screen synthesizing technique, the exposure area of a photosensitive substrate to be exposed is divided into a plurality of unit exposure areas, and exposure operations corresponding to the individual unit exposure areas are repeated, whereby a desirable pattern is finally synthesized. In the screen synthesizing technique, overlapping exposure is used in order to prevent the pattern from breaking at boundary positions of the individual unit exposure areas due to drawing errors of a reticle (mask) for projecting the pattern, distortions of projection optical systems, positioning errors of stages for positioning the photosensitive substrate, and the like. The overlapping exposure refers to exposure operations carried out such that unit exposure areas overlap each other, more specifically, edge portions adjacent each other between the unit exposure areas overlap each other. Among the unit exposure areas, parts exposed twice or more such as these edge portions are referred to as overlapping exposure parts, whereas those exposed only once are referred to as non-overlapping exposure parts.
If exposure is carried out such that edge portions adjacent each other are simply caused to overlap each other, the amount of exposure in the overlapping exposure parts will be twice or more that of the non-overlapping exposure parts, whereby the line width of junctures in the pattern may vary depending on characteristics of photosensitive agents. Also, when screen synthesizing is carried out, differences in level may occur at junctures of the pattern due to positional deviations between adjacent unit exposure areas, whereby characteristics of the device may deteriorate. When steps for superposing screen-synthesized single layer patterns in a multilayer manner are allocated to different exposure apparatus, respectively, overlapping errors of unit exposure areas in the individual layers change discontinuously at junctures of the pattern due to differences in lens distortion and positioning errors of stages among the exposure apparatus. Due to the discontinuous changes at junctures, contrast may discontinuously vary at pattern junctures in active matrix liquid crystal devices in particular, whereby the quality of device may deteriorate.
An exposure apparatus which can eliminate the foregoing inconveniences in screen synthesizing is disclosed in Japanese Patent Application Laid-Open No. HEI 6-302501, for example. In the exposure apparatus disclosed in this publication, a function capable of controlling the amount of exposure so as to yield a desirable pattern is added to a reticle blind section for determining the exposure size. This reticle blind function capable of controlling the amount of exposure is used for gradually changing the amount of exposure at overlapping exposure parts when forming an optical image such that pattern images partly overlap each other with respect to different areas on the photosensitive substrate, so as to eliminate the above-mentioned inconveniences.
Further, in the exposure apparatus disclosed in Japanese Patent Application Laid-Open Nos. HEI 6-244077 and 7-235466, a reticle blind disposed at a position substantially conjugate with a reticle is formed with a light-attenuating portion having a width of several millimeters in which transmissivity changes from 100% to 0% from the center to the outside. The overlapping exposure parts are exposed by way of the light-attenuating portion, so that the amount of exposure at the overlapping exposure parts and that at the non-overlapping exposure parts substantially equal each other.
In the exposure apparatus disclosed in Japanese Patent Application Laid-Open No. HEI 7-235466 in particular, in a light-attenuating portion formed between a light-shielding portion and an opening, a light-shielding member is formed so as to increase its density toward the light-shielding portion. More specifically, in the light-attenuating portion, a dot-like Cr (chromium) pattern having a size not greater than the limit resolution of the exposure apparatus is arranged on a glass substrate so as to increase its density toward the light-shielding portion. Also, the reticle blind is scanned at a substantially constant speed during exposure, so as to effect control such that a substantially uniform exposure amount is finally obtained throughout the overlapping exposure parts.
When no overlapping exposure is carried out, it will be sufficient if optical aberrations, setting errors, and the like in a blind imaging optical system (relay optical system for projecting the opening of a reticle blind onto a reticle) are set to influence only the inside of the light-shielding zone in the reticle if any. Therefore, while hardly adjusting aberrations in the blind imaging optical system in the illumination system, only the focusing at the time of forming an image of the opening of the reticle blind onto the reticle is adjusted.
When carrying out overlapping exposure by scanning a reticle blind, however, the illumination area on the reticle must be defined by way of linear edges of the reticle blind, for example. Therefore, it is important that blind edge images on the reticle be linear and kept from inclining with respect to a horizontal or vertical direction. For example, if distortion occurs in the blind imaging optical system (relay optical system for projecting the opening of a reticle blind onto a reticle) within the illumination optical system when overlapping exposure is carried out by first and second exposure operations, the width in overlapping exposure parts becomes uneven under the influence of distortion, whereby the amount of exposure in the overlapping exposure parts becomes uneven.
Though the distortion is exemplified in the foregoing, the amount of exposure also becomes uneven in overlapping exposure parts when other aberrations exist in the blind imaging optical system. Namely, the degree of defocusing of images varies depending on the image height of the blind imaging optical system due to aberrations such as coma, spherical aberration, curvature of field, and astigmatism. As a consequence, the illuminance in overlapping exposure parts becomes uneven, whereby unevenness occurs in the amount of exposure. Also, so-called eccentric aberration occurring due to the eccentricity of optical members within the blind imaging optical system or the like causes the amount of exposure in the overlapping exposure parts to become uneven as with the above-mentioned aberrations.
When overlapping exposure is carried out while changing the illuminance substantially linearly by way of a light-attenuating portion having the above-mentioned transmissivity distribution, the magnification between the reticle blind and the reticle, i.e., the imaging magnification of the blind imaging optical system is also important. On the reticle, an overlapping illumination portion having a width optically corresponding to the width of an overlapping exposure part to be overlapped is patterned beforehand. If the magnification of the blind imaging optical system substantially differs from its designed value, however, the width of the overlapping illumination area on the reticle may become smaller or greater than its set value (designed value). As a result, desirable overlapping exposure may not be carried out.
Even when no overlapping exposure is carried out, as in normal projection exposure under demagnification, for example, the amount of exposure becomes uneven in the exposure area if optical aberrations, setting errors, and the like occur in the blind imaging optical system, thereby failing to form a desirable pattern.
In view of the problems mentioned above, it is an object of the present invention to provide an exposure apparatus which can lower the unevenness in the amount of exposure in overlapping exposure parts and a method of manufacturing the same.
It is another object of the present invention to provide a method which can manufacture a favorable microdevice (semiconductor device, liquid crystal display device, thin film magnetic head, or the like) having a large area upon overlapping exposure by using the exposure apparatus of the present invention.
It is still another object of the present invention to provide an exposure apparatus which can lower the unevenness in amount of exposure in exposure areas, a method of manufacturing the same, and a method of manufacturing a favorable microdevice having a large area by using the exposure apparatus of the present invention.
In one aspect, the present invention provides an exposure apparatus for exposing a transfer pattern of a mask onto a photosensitive substrate in an overlapping manner, so as to expose a pattern larger than the transfer pattern of the mask onto the photosensitive substrate; the exposure apparatus comprising a light source unit for supplying illumination light and an illumination optical system for guiding the illumination light to the mask having the transfer pattern; the illumination optical system comprising an illumination area defining unit, disposed at a position substantially optically conjugate with the mask, for defining a predetermined area corresponding to an illumination area to be formed on the mask, and an imaging optical system for forming the illumination area on the mask by projecting the predetermined area defined by the illumination area defining unit onto the mask; the exposure apparatus further comprising an adjusting unit for adjusting an optical characteristic in the illumination area formed on the mask or in an exposure area formed on the photosensitive substrate.
In another aspect, the present invention provides an exposure apparatus for exposing a transfer pattern of a mask onto a photosensitive substrate; the exposure apparatus comprising a light source unit for supplying illumination light, an illumination optical system for guiding the illumination light supplied by the light source unit to the mask having the transfer pattern, and a projection optical system for projecting an image of the transfer pattern of the mask onto an exposure area formed on the photosensitive substrate; the illumination optical system comprising an illumination area defining unit, disposed at a position substantially optically conjugate with the mask, for defining a predetermined area corresponding to an illumination area to be formed on the mask, and an imaging optical system for forming the illumination area on the mask by projecting the predetermined area defined by the illumination area defining unit onto the mask; the exposure apparatus further comprising an adjusting unit for adjusting an optical characteristic in the illumination area formed on the mask or in the exposure area formed on the photosensitive substrate; the exposure apparatus satisfying an expression of 0.01 less than NA1/(NA2xc3x97xcex2) less than 6, where NA1 is the maximum numerical aperture of the imaging optical system on the illumination area defining unit side, xcex2 is the absolute value of imaging magnification of the imaging optical system, and NA2 is the maximum numerical aperture of the projection optical system on the photosensitive substrate side.
In still another aspect, the present invention provides an exposure apparatus comprising an illumination optical system including an illumination area forming optical system for forming an illumination area on a mask having a predetermined pattern, a projection optical system for projecting a pattern image of the mask onto a photosensitive substrate, and an adjusting unit for adjusting the illumination optical system; the exposure apparatus satisfying an expression of 0.01 less than NA1/(NA2xc3x97xcex2) less than 6, where NA1 is the maximum numerical aperture of the illumination area forming optical system on the light source side, xcex2 is the imaging magnification of the illumination area forming optical system, and NA2 is the maximum numerical aperture of the projection optical system on the photosensitive substrate side.
In still another aspect, the present invention provides a method of manufacturing a microdevice using the exposure apparatus in accordance with the present invention; the method comprising an illumination step of illuminating the mask with the illumination optical system, and an exposure step of exposing a transfer pattern formed in the mask onto the photosensitive substrate.
In still another aspect, the present invention provides a method of manufacturing a microdevice; the method comprising an illumination step of illuminating a mask having a transfer pattern with illumination light, and an exposure step of exposing the transfer pattern of the mask onto a photosensitive substrate in an overlapping manner; the illumination step including an illumination area defining step of defining a predetermined area corresponding to an illumination area to be formed on a mask at a position substantially optically conjugate with the mask, and an illumination area forming step of forming the illumination area on the mask by projecting the predetermined area onto the mask by using an imaging optical system; the method further comprising an adjusting step for adjusting an optical characteristic of the imaging optical system prior to the exposure step.
In still another aspect, the present invention provides a method of manufacturing a microdevice; the method comprising an illumination step of illuminating a mask having a transfer pattern with illumination light, and an exposure step of exposing the transfer pattern of the mask onto a photosensitive substrate; the exposure step including a projection step of projecting an image of the transfer pattern of the mask onto the photosensitive substrate by using a projection optical system; the illumination step including an illumination area defining step of defining a predetermined area corresponding to an illumination area to be formed on the mask at a position substantially optically conjugate with the mask, and an illumination area forming step of forming the illumination area on the mask by projecting the predetermined area onto the mask by using an imaging optical system; the method satisfying an expression of 0.01 less than NA1/(NA2xc3x97xcex2) less than 6, where NA1 is the maximum numerical aperture of the imaging optical system on a side opposite from the mask side, xcex2 is the absolute value of imaging magnification of the imaging optical system, and NA2 is the maximum numerical aperture of the projection optical system on the photosensitive substrate side; the method further comprising an adjusting step of adjusting an optical characteristic of the imaging optical system prior to the exposure step.
In still another aspect, the present invention provides a method of manufacturing a microdevice; the method comprising a step of illuminating a mask having a predetermined pattern by using an illumination optical system including an illumination area forming optical system for forming an illumination area on the mask, a step of exposing a photosensitive substrate by using a projection optical system for projecting a pattern image of the mask onto the photosensitive substrate, and a step of adjusting the illumination optical system; the method satisfying an expression of 0.01 less than NA1/(NA2xc3x97xcex2) less than 6, where NA1 is the maximum numerical aperture of the illumination area forming optical system on a light source side, is the imaging magnification of the illumination area forming optical system, and NA2 is the maximum numerical aperture of the projection optical system on the photosensitive substrate side.
In still another aspect, the present invention provides a method of manufacturing an exposure apparatus, comprising an illumination optical system for illuminating a mask having a transfer pattern with illumination light, and a projection optical system for projecting a transfer pattern image of the mask onto a photosensitive substrate, for exposing the transfer pattern of the mask onto the photosensitive substrate in an overlapping manner so as to expose a pattern larger than the transfer pattern on the mask onto the photosensitive substrate; the method comprising an aberration correcting step of correcting a rotationally asymmetrical aberration or decentering aberration remaining in the illumination optical system, and an adjusting step of adjusting an optical characteristic deteriorated by the aberration correcting step.
In still another aspect, the present invention provides a method of manufacturing an exposure apparatus, comprising an illumination optical system for illuminating a mask having a transfer pattern with illumination light, and a projection optical system for projecting a transfer pattern image of the mask onto a photosensitive substrate, for exposing the transfer pattern of the mask onto the photosensitive substrate; the method comprising an aberration correcting step of correcting a rotationally asymmetrical aberration or decentering aberration remaining in the illumination optical system, and an adjusting step of adjusting an optical characteristic deteriorated by the aberration correcting step; the method satisfying an expression of 0.01 less than NA1/(NA2xc3x97xcex2) less than 6, where NA1 is the maximum numerical aperture of an imaging optical system included in the illumination optical system on a side opposite from the mask side, xcex2 is the absolute value of imaging magnification of the imaging optical system, and NA2 is the maximum numerical aperture of the projection optical system on the photosensitive substrate side.
In still another aspect, the present invention provides a method of manufacturing an exposure apparatus comprising an illumination optical system for illuminating a mask having a transfer pattern with illumination light, and a projection optical system for projecting a transfer pattern image of the mask onto a photosensitive substrate; the method comprising a measuring step of measuring an optical characteristic in an illumination area formed on the mask or an exposure area formed on the photosensitive substrate, a first aberration correcting step of correcting a rotationally symmetrical aberration remaining in the illumination optical system according to a result of measurement obtained by the measuring step, and a second aberration correcting step of correcting a rotationally asymmetrical aberration remaining in the illumination optical system according to a result of measurement obtained by the measuring step.
In still another aspect, the present invention provides a method of manufacturing an exposure apparatus for exposing a pattern formed in a mask onto a photosensitive substrate; the method comprising the steps of installing an illumination optical system including an illumination area forming optical system for forming an illumination area on the mask, installing a projection optical system for projecting a pattern image of the mask onto the photosensitive substrate, measuring an optical characteristic of the illumination optical system, and adjusting the illumination optical system; the method satisfying an expression of 0.01 less than NA1/(NA2xc3x97xcex2) less than 6, where NA1 is the maximum numerical aperture of the illumination area forming optical system on the light source side, xcex2 is the imaging magnification of the illumination area forming optical system, and NA2 is the maximum numerical aperture of the projection optical system on the photosensitive substrate side.